Conventionally, as a fluid separation element used for reverse osmosis filtration, micro filtration, or the like, a spiral membrane element is known which is provided with a cylindrical roll R in which a separation membrane 1, a feed-side flow passageway member 2, and a permeate-side flow passageway member 3 are spirally wound in a laminate state around a perforated center tube 5 and in which sealing parts 11 to 13 for preventing mixing of feed-side fluid and permeate-side fluid are disposed, for example, as shown in FIG. 5.
In this spiral membrane element, the feed-side fluid (feed water) is led to the separation membrane 1 surface by the feed-side flow passageway member 2 and, after being separated by permeating through the separation membrane 1, the permeate-side fluid (permeated water) is led along the permeate-side flow passageway member 3 to the center tube 5 (water collection tube). Then, in such a spiral membrane element, there are cases in which a fiber reinforced plastic (FRP) is disposed on the outer circumference as an external material for the purpose of imparting a pressure resistance property and a shape retaining property at the time of pressurization operation (illustration is not given).
As shown in FIGS. 6(a) to (b), such a spiral membrane element is produced generally by fabricating a separation membrane unit U by stacking a material in which a feed-side flow passageway member 2 is disposed between the two sheets of a two-folded separation membrane 1 onto a permeate-side flow passageway member 3, and applying adhesives 4 and 6 for forming a sealing part that prevents mixing of feed-side fluid and permeate-side fluid to the permeate-side flow passageway member 3 located on the separation membrane peripheral parts (three sides), and spirally winding a single or a plurality of this unit U around a center tube 5, followed by sealing the separation membrane peripheral parts. This example is a case in which a plurality of membrane leaves (sealed envelope-shaped membrane) is present; however, there are cases in which a single membrane leaf is present.
Also, for forming the external material, there is known a process in which, generally after the membrane leaf is wound on the center tube and the sealing resin is hardened, a glass roving (an assembled body made of strands of glass filaments) impregnated with a resin is wound around the outer circumferential surface of the cylindrical roll, and this is hardened and formed as an FRP (for example, see the patent documents 1 to 2).
However, with the above-described process, the external material is implemented after winding the membrane leaf and sealing, thereby necessitating a step of winding the external material and a hardening step in addition to the hardening-waiting time for sealing. In particular, it is a cumbersome and time-consuming step to perform winding so as to obtain a uniform reinforcement effect in winding the glass roving impregnated with a resin. For this reason, with the above-described process, the production step becomes complex, requires a long period of time, and is disadvantageous in terms of costs including the matter of materials.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-17840    Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2000-354742